Grebe, 74, made the announcement in a recent letter to supporters of the Milwaukee-based foundation. He was named CEO and president of the $850 million foundation in 2002.

"Next Sunday, I'm going to be celebrating my 75th birthday," Grebe said Thursday, adding that the milestone led him to reflect on his life and career.

"I still love the job, and because I'm fortunate to be in very good health, I could continue to do it for several more years," Grebe continued. "But this just seems to me like a good time to move on. So I told our board a couple of months ago that I wanted to retire next year."

Grebe, who earned two Bronze Stars in Vietnam, long was a lawyer at Foley & Lardner in Milwaukee, eventually becoming chairman and chief executive officer of the firm.

He said he will not be stepping away from his involvement in Republican Party politics.

"I'm not capable of that," said Grebe, who has served as the chairman of Gov. Scott Walker's state campaign committee since 2009 and Walker's failed presidential campaign this year. Grebe previously served as general counsel to the Republican National Committee.

Grebe received a salary of $518,240, plus $318,881 in retirement and other benefits, from Bradley in 2013, the last year for which federal records are available.

Cleta Mitchell, a Bradley board member, said Grebe will leave behind a legacy of expanding the foundation's reach and influence as the group helped underwrite conservative groups and individuals around the country.

"The Bradley Foundation is now the leading conservative grant-making foundation in the country, probably the world," said Mitchell, who worked with Grebe at the Foley law firm. "It's pretty remarkable."

Named for Lynde and Harry Bradley, who helped found Milwaukee's Allen-Bradley Co., the foundation has been a primary source of income for some of the biggest and most influential conservative think tanks and nonprofits over the past three decades.

Among past recipients have been the Heritage Foundation, the American Enterprise Institute, the American Legislative Exchange Council and the Federalist Society— all trying to put their stamp on the three branches of government.

Millions more have gone to just about every major conservative publication, including such magazines as Reason, Crisis, First Thingsand National Affairs.

Ideologically, Bradley has underwritten the groups that define and defend bedrock economic, educational and foreign policy issues within the conservative movement.

Bradley dollars flow to groups that favor curtailing the influence of unions, promoting school choice legislation, deregulating campaign finance laws and strengthening American defense — ideas often embraced by Walker and other Wisconsin politicians.

Locally, the foundation has given millions of dollars for arts, education and civic groups, ranging from the Milwaukee Symphony Orchestra to School Choice Wisconsin.

Under Grebe's leadership, Bradley became more directly involved in media and politics.

The group has, for instance, helped jump-start such Wisconsin-based conservative online media outlets as Media Trackers and Wisconsin Watchdog. Grebe has also played host at an annual gala in Washington, D.C., in which the foundation gives $250,000 grants to four or five pundits and opinion leaders for their role in advancing the conservative cause.

Not everyone is happy with Bradley's growing influence under Grebe.

"The Kochs are getting a lot of attention, but Michael Grebe has long been the ghost in the machine as a top funder of the right-wing infrastructure," said Mary Bottari, deputy director of the left-leaning Center for Media and Democracy.

Bottari said the foundation has lost credibility for its role in setting up front groups, attack-dog media outlets and fake grass-roots organizations.

"Michael Grebe took the $800 million-plus he controlled as head of the Bradley Foundation and integrated it into the fabric of state and national GOP politics — promoting right-wing policies (and) defending favored politicians," said Mike Browne, deputy director of the liberal group One Wisconsin Now, a group that tracks Grebe and Bradley's activities.

But Grebe said Thursday that he has always kept his work at the foundation separate from his political involvement.

"That is totally unrelated," he said.

At a Thursday afternoon news conference, Walker had kind words for his campaign chairman, telling Journal Sentinel reporter Mary Spicuzza that Grebe has played a "key role" in Walker's campaign over the past five years.

Walker's close ties to the organization were made clear when just days after he was first elected governor, he met privately with Bradley's board and senior staff at Bacchus, a swanky Milwaukee restaurant.

But the Republican governor made it clear on Thursday that he isn't interested in replacing Grebe at Bradley. Walker said he was happy in the governor's mansion.

Dennis Kuester, the former chairman of M&I Bank and now Bradley board chairman, said the board has already retained a search firm to help find Grebe's successor. Grebe is only the second CEO of the 29-year-old foundation, having replaced Michael Joyce.

Kuester emphasized that the foundation will remain in Milwaukee and its next leader will reside here.

Mitchell, the Bradley board member, said the next CEO of the foundation will face a tall task, noting that Grebe has left a "large footprint."

"Mike is such a great combination — philosophical, conservative, leadership skills, and he has that political gene. He's multifaceted and has all of the attributes," Mitchell said. "I don't think it's going to be easy to find another person with all those."